How to change the shortcut (F) to resize the brush in sculpt mode
You have to go in the "Blender Preferences" and under "Keymap" select search by "Key-Binding".

Then click in the middle of the list to be able to scroll down and search for the first entry under Sculpt

The open one is the one for the basic resize with F, so you can just click on the field i marked red to then assign a new key means click on it, then press S.
If you want to keep the functions on the same button for the different types of resize, then i'd recommend to assign the S key to the 2 other "Radial Control"s. Do only click again on the same area as before and press S, the modifier keys in the column below like Shift, Ctrl, Alt and Cmd stay the same as long as you do not click them.

It should then look like this after the change:


Happy Blending